1. Field of the Invention:
This invention relates generally to static VAR generators and more particularly to static VAR generators utilizing anti-parallel thyristors for inserting reactors for network stability and power factor correction having thyristor circuit surge protecting means.
2. Description of the Prior Art:
In static VAR generators using anti-parallel thyristors for switching of reactors into an AC network or for controlling the current through the reactors for the purposes of power system stability and power factor correction, abnormal conditions sometimes occur in the system where transient currents may pass through the thyristor circuits that greatly exceed the current rating of the thyristor banks damaging the thyristors and inhibiting the reliability of the system. It would be desirable to limit the current passing through the thyristor circuits in the event of such current surging conditions. Some methods employ lower cost mechanical switches in a shunt circuit arrangement so that surging currents would not pass through the thyristor array. However, in such situations the thyristors array is short-circuited eliminating the current required to turn the thrystor arrays back on to maintain the reactors in the AC network after the transient conditions have passed and before the shunt is removed. Thus it would be advantageous to have a static VAR generator utilizing lower cost mechanically switched shunt circuits that will still allow operation of the thyristor arrays to turn on after the occurrence of transient surge current. A further advantage could be realized if the mechanical switch in the shunt circuit could be opened or closed only when the thyristor array was conducting. This would allow the use of a switch having lower voltage and current ratings.